Recovery of formation fluids, especially petroleum from subterranean formations is frequently difficult when the subterranean formation is comprised of one or more incompetent or unconsolidated sand layers or zones. The sand particles in the incompetent or unconsolidated sand zones move or migrate into the wellbore during the recovery of formation fluids from that zone. During the production of petroleum from wells completed in formations containing unconsolidated sand, the movement of sand into the wellbore can cause the well to cease production of fluids therefrom after a relatively short period of time. The small sand particles plug small openings in sand restraining devices placed on the end of the production tubing in the wellbore such as screens or slotted liners. The accumulation of the sand along the small openings cause the production of fluid to be reduced or stopped altogether. Moreover, sand particles often flow through the openings in the screens and are produced to the surface of the earth, where they cause considerable mechanical problems because of their abrasive nature, leading to early failure of pumps and other mechanical devices used in the production of petroleum.
Many techniques have been described in the prior art for preventing or decreasing the flow of sand into the well during the course of petroleum production, including sand screens, filters, perforated or slotted liners, incorporated in the well. These prior art techniques have been successful in limited instances, but are seldom entirely satisfactory for a number of reasons. The mechanical devices usually restrain only the larger sand particles that are not completely effective for the purpose of restraining or preventing the flow of fine particles from the formation into the well and ultimately to the surface. Such devices have a relatively small filter area and so tend to become plugged quickly. Furthermore, these devices are expensive and they interfere with various types of completion and workover operations which are routinely applied to producing oil wells.
Chemical compositions have been described in the literature which can be injected into subterranean formations to bond the sand grains together, using a resinous plastic material which forms a permeable mass within the formation itself immediately surrounding the portion of the formation from which fluid production is being taken. These methods usually involve injecting into the unconsolidated sand around a wellbore, a polymerizable, resinous material which is later caused to polymerize so as to consolidate the formation sand in order to form the desired fluid permeable mass which restrains the flow of sand particles. Numerous difficulties have been encountered in commercial application of these techniques, including the difficulty of achieving even polymerization of the resinous material to the degree necessary to consolidate the sand particles while still maintaining the necessary permeability so the petroleum or other fluids may pass freely from the formation through the consolidated mass into the well. Furthermore, these materials are expensive.
Numerous previous publications including our copending application Ser. 07-357-571 filed May 30, 1989, now U.S. Pat. No. 4,903,770 for Sand Consolidation Process, and U.S. Pat. No. 4,842,072 issued June 27, 1989 for Sand Control Method, describe processes using monomers or oligomers of furfuryl alcohol in combination with an ester and an acid catalyst to form a sand consolidating, polymerized matrix in a formation adjacent to an oil well to restrain the flow of sand. These processes have been used with success in numerous oil fields and found to produce consolidations which are tough and durable and exhibit unique temperature stability. The acid catalyst incorporated in the treating fluid causes reaction times well suited to placing the fluid in the formation and having the polymerization occur at precisely the correct time, so the treating fluid is located where the consolidation is needed, adjacent to the producing well, providing the formation temperature is at least 200.F. At temperatures lower than 200. F, the reaction rate is so low that the treating fluid tends to leak away from the zone where consolidation is desired, resulting in a low quality consolidation result, or even a total failure.
In view of the foregoing discussion, it can be appreciated that there is a substantial, unfulfilled need for a method for consolidating unconsolidated sand in subterranean petroleum containing formations to form a permanent, permeable barrier which allows the passage of fluids through the barrier while restraining the movement of sand, employing the highly effective furfuryl alcohol, in formations whose temperature is below 200.degree. F.